HR: 1340h
AN: SM33A-1116    [Abstracts]
TI: Pi2 modulation of aurora as observed by all-sky TV image and magnetometers on board two geosynchronous satellites
AU: * Saka, O
EM: saka.o@nifty.com
AF: Office Geophysik, 1165-1 Ogoori, Ogoori, 838-0141, Japan
AU: Hayashi, K
EM: QYI05527@nifty.ne.jp
AF: University of Tokyo (retired), 7-3-1 Bunkyou-ku, Tokyo, 113-0033, Japan
AB: We analyzed the auroral event of January 24 1986 using all-sky TV images and magnetometer data from two geosynchronous satellites (Goes5 and Goes6) separated by 2 hours of local time. From those analyses we found that poleward expansion of aurora following the auroral onset by 1 min was accompanied by surface waves excited in the midnight sector. The surface waves demonstrated out-of-phase relation in the D component (dipole east) and in-phase relation in the V component (radial outward) at GOES5 and GOES6 meridians, respectively. The oscillations in V-D plane led to CCW polarizations in the dawn side of aurora and CW polarizations in the dusk side. Simultaneous observations of those polarization patterns by ground magnetometers in auroral zone suggested an FLR structure in the midnight magnetosphere. We found that auroras ignited between GOES5 and GOES6 meridians were intensified when the largest eastward and westward bending of field lines occurred in the dawn and dusk side of aurora. The latitudinal extent of auroral modulations by surface waves expanded in geomagnetic latitudes up to 70N. Surface waves excited in the midnight magnetosphere might act as possible wave energy sources for auroral acceleration regions in lower altitudes. Those surface waves may also be a driving source of slow shock that supplies kinetic energies (bulk plasma flow) directly to the acceleration regions. A slow shock model based on double adiabatic equations of state was constructed. This theoretical model showed that although slow shock cannot carry particles having pitch angle distributions that are peaked perpendicular to the field lines, slow shock carry particles having isotropic pitch angle distributions. It is supposed that magnetic mirror force is responsible for this effect.
DE: 2407 Auroral ionosphere (2704)
DE: 2716 Energetic particles: precipitating
DE: 2752 MHD waves and instabilities (2149, 6050, 7836)
DE: 2790 Substorms
SC: SPA-Magnetospheric Physics [SM]
MN: 2007 Fall Meeting